Co-circulation of lineage 1 and lineage 3 porcine reproductive and respiratory syndrome virus type 2 (PRRSV-2) in Taiwan during 2018–2024

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a major concern in swine production. This study investigates the molecular epidemiology of lineage 1 and lineage 3 PRRSV-2 in Taiwan between 2018 and 2024. A total of 43,977 samples were collected across 15 counties in Taiwan, and 13,611 tested positive for PRRSV by real-time PCR. Among of them, 501 complete ORF5 sequences were determined and analyzed. The identified PRRSV-2 sequences belonged to either lineage 1 (specifically sublineage L1A which could be divided into at least Clade A, Clade B, and Clade C; 117/501, 23.4 %) or lineage 3 (384/501, 76.6 %). Surprisingly, among the 117 lineage 1 PRRSV-2 sequences, 103 (88.0 %) were from sow-related specimens whereas only 14 (12.0 %) from nursery pigs. Phylogeographic data revealed multiple bidirectional transmissions between central and southern Taiwan, followed by spread to the northern and eastern regions. This imply that the lineage 1 PRRSV-2 caused high mortality and abortion rates in sows and has spread to the entire Taiwan island. The present study provides the first description of the current epidemic state and spread of foreign lineage 1 PRRSV-2 strains in Taiwan during 2018-2024.